1. Field of the Invention
The present invention relates to a piercing method which makes it possible to enable unskilled operators to operate a laser beam machine, maximize machining quality and productivity for each material and workpiece thickness, accomplish long, unattended operation, and perform piecing preferentially with a special-purpose piecing torch.
2. Description of the Related Art
According to conventional machining methods, machining programs are created by adding machining conditions such as laser intensity, feed rates, piecing conditions to predetermined machining geometries and then machining is performed by specifying one or more created machining programs for material.
When machining predetermined geometries from the middle of material rather than end of the material, holes are pierced at machining start points in the material in order for a laser beam and assist gas to pass the material (hereinafter this process is referred to as “piercing”) before starting machining, and then the predetermined machining operations are performed according to the machining programs (hereinafter this process is referred to as “cutting”).
When laying out multiple machining geometries with the best yield rate (hereinafter this process is referred to as “nesting”) and machining individual geometries, piercing and cutting are performed alternately. Besides, if workpiece thickness is large, piercing takes a long time, building up heat and resulting in machining defects.
Also, when small machining geometries are involved, heat builds up during piercing and cutting, resulting in machining defects.
On the other hand, a method is known in which piercing and cutting are performed by adjusting focal distance according to machining programs (Japanese Patent Laid-Open No. 7-223084 or Patent Document 1).
Generally, optimum machining conditions for piercing and cutting do not coincide. If piercing is optimized, cutting is not optimized. If cutting is optimized, piercing is not optimized. Since a compromise is sought between piercing and cutting, it is impossible to perform both piercing and cutting using optimum values and thus it is impossible to optimize machining quality and productivity.
Also, if piercing is not optimized, piercing takes a long time. This not only reduces productivity, but also causes heat build-up in the workpiece, which in turn will cause machining defects such as degradation of machining quality or even disable machining.